Milage is my main concern. I'm running a 2.8 paired with a 4T60 auto, so I should be getting somewhere in the neighborhood of 20 in town and 30-35 highway. The best I've pulled has been 24 highway.

I'm not getting any rich running errors from the ECM and it idles ok, maybe a tad bit on the high side till it warms up but I think thats normal.

I've had the distributor in and out 3-4 times now and each time of re-adjusting the timing hasn't done anything to affect the fuel economy. I did put the motor into diagnostic mode first.

The converter has been replaced on the car before I got it by a previous owner. I can only assume its good but I seem to have decent air flow at the exhaust tips. I actually have an ALDL cable that I've tried to use with my Buick. I'll have to dig it out and see if I can get it to work on the Fiero.

I actually blocked off the cold start injector. I didn't have the metal line for it when I put the motor together so I just have it all blocked off. So, no leaks there. Its the cause of my hard cold starts but after the car is warm and running it'll restart fine.

So needless to say, this is driving me nuts. I think the next best thing to check is the injectors for leaks. I could pull the regulator off at the same time and visually inspect it for leaks as well.

I don't like throwing parts at an engine but I also don't like going crazy trying to figure out whats not working right :P

Without going back through your thread and finding out first, have you tested your thermostat? If the coolant is circulating too much, the engine takes longer to warm up to optimum operating temperature. This can kill your mpg.

Jonathan

I'm on my second thermostat with no changes in MPG either...

I believe I started with a 180* Stant and then went back to a 195* Stant. New coolant temp sensor too.

Have you looked at rolling resistance? Tire pressure, alignment, wheel bearings, dragging brakes?

Jonathan

New calipers front and back, tire pressure is kept up around 40-43 PSI, Its had an alignment since I got it running again, new rear bearings and the fronts have been repacked.

Its maddening ...

So I finally found my 12 point 10mm socket. But now its cold. And its late. I dunno, I may put off pulling the intake till tomorrow unless I decide I'm crazy.

your fuel pressure should not drop off quickly like that but it is very encouraging to see that you in fact are getting a steady 40psi while the eng is running. My stock 86GT auto gets 20-22mpg with reasonable driving. I would expect you to get better than mine but how much better may be a bit subjective. I am not sure that you are too far off. Good luck. May the wx warm up soon...

Charlie

[This message has been edited by cptsnoopy (edited 03-12-2010).]

Right, I figure if I'm getting good pressure with the motor running that the pump is working as it should at least. If the fuel is just leaking back via the pump, then thats ok. But if its leaking past the injector(s) or the regulator, then I've got problems.

I figure I should be pulling better economy but the car did start as a basketcase so I guess I'll just have to try to eliminate one thing at a time. I've considered buying Rodney's metal vacuum lines and auto trans shift cable just to eliminate those as possible issues but I just don't have the cash for them right now.

Can you do a compression check to see if you have any sealing problems.

You said before you though it was sluggish, but I didn't see any clairification of sluggish. Just kinda sluggish, and non specific? With you detailed discription, I'm assuming you didn't leave off a more specific sluggish trouble.

Yeah you have tried a lot, it would makes sense to at least look at the possibility of leaking injectors.

Shift points on the tranny seem about right? Its locking up in high gear? Can you tell if it is? A "normalish" final gear ratio?

You might want to try the "pull the O2 sensor" trick to see if there is a possibility of blockage on your cat. If your sluggishness is only slight, pulling the O2 sensor might not make much of a difference. Having the O2 sensor puts the engine in limp mode so that messes up your mileage so you couldn't drive it long enough to see if that changed your mileage.

If your sluggishness is noticeable enough you might also want to just try disconnecting the O2 sensor wireing, and see if there is a noticable improvement when the engine is in limp mode. If so that would most likely mean a sensor is out of wack, putting the ECM out of wack when your in closed loop mode.

[This message has been edited by phonedawgz (edited 03-12-2010).]

The o2 sensor is fairly new at least. I'd have to rent the tools to do the compression test but I could do one. I'm actually curious to see how worn out this motor is myself. The block has around 100k on it and ran before it was swapped out for a 3.4, at least thats what I was told when I got it.

Sluggish just means that its a bit on the slow side to accelerate and go through the gears. Part of the problem is that I have a 4t60 geared for 2.84 (granny gearing) but I'm not sure if my TV cable is any good as I can't seem to make it "ratchet" when I try to adjust it. The shift points sometime feel like they come too late, but its hard to tell because my tach has been really flaky ever since I've had the car running. I'm pretty sure its going into lockup, but not entirely.

I think I'm going to pull the intake after class to check for leaky injectors. If that doesn't work, I'll try unplugging the O2 sensor and see if the car seems to run any better in default settings. I need to dig out my ALDL cable too and see if I can get WinALDL to work... maybe that will be enlightening somehow?

Yeah, I'm not suspecting the O2 sensor is bad. Seeing if the very sluggish performance improves quite a bit is a way to troubleshoot a plugged Cat converter. I am not thinking thats whats happening with yours with the new info.

Having it just electrically unplugged is also a way to see if theres a problem when the engine is running in the "closed loop" condition. Leaving it unplugged forces the engine to run in the "open loop" aka "limp" mode.

The ALDL would tell you if the sensors are seeming to be working correctly. A bad sensor can make the computer tune the engine way out of what it should be

Late shifting on the tranny - surely could be causing bad mileage - I think you should look at how thats working, and see if you can get it figured out. Your tranny I have no experence with.

Might as well check the injectors - if nothing else eliminate them. Who knows you might find the trouble there.

If you do the compression check, also take note of all the spark plugs for how the cylinders are running .

Any one else for ideas???

I'm going to be heading to my girlfriends place for a few days so maybe I'll pull the rail off while I'm there. The weather is supposed to be crappy too though so we'll see. I think that when I get some extra money that I'm going to go ahead and replace the TV cable and maybe the vacuum lines just to get rid of the crappy plastic lines.

So I just pulled my top intake off. No fuel coming out of the injectors or the regulator. Just for the heck of it I pulled the regulator apart and found no fuel in the top half that is ran off of vacuum.

I'm priming the pump and getting 47 psi, then it quickly drops down to about 10 and slowly bleeds down to zero in about five minutes. However, not every time I turn the key to "on" does it prime. Is there something in the ECM that only primes the pump every few seconds so as not to blow out the regulator? Looks like its bleeding down from the pump itself then... its a new pump though? Should I replace it or is it ok as it seems to hold steady at about 40-41 while the car is running?

Another problem that seems to be getting worse is a "shake" at about 60mph after I've been driving the car for a while. It feels almost as it its trying to shift into a higher gear. I noticed that the TV cable seemed to fit rather loose in the thottle body so I think I'm going to try to re-adjust it.

I also managed to break a vacuum line taking off the intake, or at least I think I broke it this time... maybe its been broken all along and has been the source of my trouble? I doubt I'm that lucky...

I'm really tempted to just go ahead and buy Rodney's TV cable and metal vacuum lines just to be able to eliminate those two as potential problems.

35mpg might be a tad optimistic on winter fuel blends. My little '95 Honda Del Sol with a 1.6L engine has dropped from it's normal 30mpg to around 24mpg in town this winter.

Perhaps a leak in the connection between the fuel pump and the steel tubing? Are you using the pulsator or are you using a piece of fuel line for that connection? Other than that just the slim possibility that the fuel pump check valve is faulty.

Charlie

Yeah, I know winter blend sucks. But the best I've pulled on the highway has been 23 with my 4T60. I should get closer to 30, especially since its been closer to 15-18 the last several months.

Anyway, I might have found part of the problem with the TV cable being out of adjustment. I'm having trouble getting it adjusted as the button is damn near impossible to press without pliers. I pulled the cable out, pressed the button, and pulled the cable all the way in (the plastic sheathe is all the way towards the PS of the car) and took a drive. Shifting from 1 to 2 took very high RPM's but I seemed to have really good acceleration and shifting up through to 70mph or so.

I thought that the TV cable would "ratchet" to adjust when I pressed the accelerator, but no go. It wouldn't ratchet out so I managed to get the button to sorta press enough for the cable to slide forward some. I haven't driven it again, but I need to find a small C clamp to press the button while I adjust the cable in and out to get it set right.

The fuel pump came with a piece of hose to replace the pulsator... I suppose I should have just re-used the pulsator but meh. I did use hose clamps so I wouldn't think it would leak and the fuel line should have been the correct stuff. Dunno though... it must be the check valve in the pump. I didn't use an AC Delco or Delphi pump as I probably should have, but I used a "TRE Performance" pump as recommended in a couple other threads on here. They're supposed to be good quality and I think I'll be ok since my Harbor Freight pressure gauge says I'm pulling 40-41 PSI at idle.

[This message has been edited by Alibi (edited 03-19-2010).]

You should NOT be pulling 41 psi at idle. You should have about 41 before the engine starts OR with the vacuum line disconnected. The fuel pressure should be 34-45 psi BEFORE starting. After starting the regulator connected to the intake is SUPPOSED to drop the pressure to an amount equal to the intake vacuum thus making the differential from the pressurized side of the injector to the intake side of the injector to be the same. If the fuel pressure isn't varying with the intake pressure the first suspect would be a disconnected vacuum line.